In the context of many applications employing binding molecules, e.g. for therapeutically active antibodies directed to a target in an animal or human, there is a need for methods which enable the determination of such target in the presence of the binding molecule, without the requirement to remove the binding molecule prior to determining the amount or concentration of the target. In particular for e.g. therapeutically active antibodies or therapeutically active receptors or receptor fragments, there is a need for in vitro methods which allow the determination in bodily samples of the total amount or concentration of the target against which the therapeutically active antibody or therapeutically active receptor or receptor fragments is directed, without removing from the sample the therapeutically active antibody or therapeutically active receptor or fusion protein. The total amount thereby comprises both free, unbound target, and target bound to the therapeutically active antibody or therapeutically active receptor or receptor fragments.